The prior art has recognized the desirability of fuel savings by turning off electric air conditioner units or heater units when rooms become unoccupied. Power savings becomes an important criterion of profitable operation, particularly in the hotel/motel industry, where a guest may check out early in the morning leaving the air conditioner or heater unit fully operative, and this may not be remedied until the room is readied for a new occupant by a maid in the late afternoon.
In order to justify retrofit of an in-room system to one which automatically senses the occupancy and shuts off the power to the heater-cooler unit when there is no occupancy, the cost of the retrofit units and the installation costs are critical. In other words the costs of the conversion must pay for itself within a relatively short time period, preferably no longer than a year, in order to justify the outlay for the retrofit.
The prior art fuel saving systems are not well adapted for retrofit. For example, they have problems of interfitting with different kinds of basic installed systems with no standard configuration. This means customization of retrofit systems for different kinds of in-room units at a high equipment and wiring cost. Furthermore, if an installed system is retrofitted with an auxiliary control unit there is a problem of system communication between the basic system and the auxiliary control unit without interference with the system functioning, and the necessity for system design changes, with corresponding high electric connection costs.
The prior art conversion equipment cost for a retrofit installation thus is a significant problem that has not satisfactorily been resolved. For example, completely automatic temperature control is an expensive feature in prior art control units, requiring a thermal sensor and a corresponding temperature correction system to maintain a desired temperature level. Furthermore the initial conversion cost is significant, requiring expert electrician labor, in order to make a retrofit unit compatible with the wiring and functioning of the in-room unit in service.
Systems requiring a comprehensive computer control system are too expensive for use in retrofit of a single in-room temperature control system, for example. Furthermore such systems are not easily maintained or repaired when malfunctioning.
Functional performance is also critical in the prior art. Accordingly problems complex multiple sensor control systems or critical placement of sensors within the room for detecting occupancy can produce unacceptable functional performance.
Some systems of the prior art rely upon manual intervention, which because of human errors and lack of action cannot give satisfactory performance for optimizing fuel savings.
These problems in the prior art are exemplified in the typical U.S. patented art now discussed. E. A. Carrell, et al., U.S. Pat. No. Re. 33,146, Jan. 16, 1990 for Occupancy Responsive Temperature Control System, relies upon a door switch which requires the manual opening and closing of a door. J. C. Grimes, et al., U.S. Pat. No. 4,101,866, Jul. 18, 1978 for Apparatus for Conserving Energy in Electrical Appliances, also relies upon manual actuation to work a dead bolt switch in the door for reset of the system after an occupant returns. These systems are not fully automatic, nor reliable, since a door or a dead bolt may be left open by an occupant thus causing system malfunction.
It is critical in the motel/hotel industry to provide comfort to the guest occupants without involving complex adjustments, and many systems thus are unacceptable because the guests may not find their quarters at proper temperature when unreliable or complex systems malfunction. Furthermore, guests are not patient with systems that require critical operating adjustments.
R. H. Beerbaum, U.S. Pat. No. 5,127,575, Jul. 7, 1992 for Supervisory Control Unit for Electrical Equipment and D. R. Schulz, U.S. Pat. No. 4,433,809, Feb. 28, 1984 for Controller for Air Conditioning or Heating System require thermostatic controls that are critical in operation, costly and wasteful because of redundancy of ensuing controls. This can cause malfunctions and interference with built-in thermostatic control systems resulting in guest discomfort. A. Dytch, U.S. Pat. No. 4,462,540, Jul. 31, 1984 for Control System for an Air Temperature Changing Unit similarly requires a temperature sensing controls in addition to thermostatic controls available in the air conditioner unit, so that there is probable interference and overlap of the automatic temperature control system, and a necessity to coordinate the relative functions of more than one temperature control sensor. Extra apparatus is not only expensive but adds to the unreliability of the system and probably complexity in setting operating controls.
In addition, the Dytch system is typical of control units that may give false responses representative of occupancy and thus are not capable of responding accurately to the occupancy of rooms by guests that require temperature controls. Thus, the Dytch sound detection method of occupancy sensing is subject to many kinds of false signals, such as from knocks on the door and neighbor's sounds that pass through the walls, and other extraneous noises that may occur to thus disrupt the theoretical savings of power during room unoccupancy.
If a room is unoccupied for long periods of time under extreme temperature conditions, pipes may freeze or the rooms may be too warm for immediate occupancy by a guest. Thus, it is desirable in an automatic system that there be a compatible manner of conforming to long term requirements as well as short term requirements with enough flexibility to satisfy the needs of various hotel/motel proprietors during long periods of unoccupancy, for example.
Thus, it is a general objective of the invention to provide a simplified fuel savings control system, which is easily installed for retrofit use and inexpensive, and yet is fully automatic for control of heater/cooler system power consumption room by room based upon occupancy of the rooms.